International Journal of Universal Computer Sciences (Vol.1-2010/Iss.2) Elboukhari et al. / Quantum Key Distribution Protocols: A Survey / pp. 59-67 Quantum Key Distribution Protocols: A mmm Survey Mohamed Elboukhari*, Mostafa Azizi**, Abdelmalek Azizi*,*** *dept. Mathematics & Computer Science, FSO, University Mohamed Ist, Morocco [email protected] **dept. Applied Engineering, ESTO, University Mohamed Ist, Oujda, Morocco [email protected] ***Academy Hassan II of Sciences & Technology, Rabat, Morocco [email protected] Submitted: 22/02/2010 Accepted: 23/03/2010 Appeared: 30/03/2010 HyperSciences.Publisher Abstract—Most cryptographic mechanisms, such as symmetric and asymmetric cryptography, often involve the use of cryptographic keys. However, all cryptographic techniques will be ineffective if the key distribution mechanism is weak. The security of most modern cryptographic systems of key distribution mechanism is based on computational complexity and the extraordinary time needed to break the code. Quantum Key Distribution (QKD) or Quantum Cryptography is attracting much attention as a solution of the problem of key distribution; QKD offers unconditionally secure communication based on quantum mechanics. In this article we survey the most popular QKD protocols. Also, we give a short state of the art of Quantum Cryptography. Keywords: Quantum Cryptography, ey distribution, Quantum Key Distribution protocols. m 1. INTRODUCTION A cryptosystem of asymmetric encryption operates by handling two keys: secret and public. Each participant The security has become a big concern in wired and wireless diffuses a public key with his name. If one wishes to networks. The characteristics of networks pose both communicate with a participant, it is necessary to recover his challenges and opportunities in achieving security goals, such public key and cipher with it the message, and send the as confidentiality, authentication, integrity, availability, ciphered message to this participant which is the only person access control, and no repudiation. Cryptographic techniques who knows the secret key which makes possible to decipher are widely used for secure communications. the received messages. The secret key is of course related to the public key, in practice by a mathematical relation. The Cryptography is composed schematically by two systems: power of the security of these cryptosystems is based on symmetric encryption and asymmetric encryption. algorithmic complexity; it is difficult in practice to deduce the secret key from the public key in a reasonable delay. The cryptosystems of symmetric encryption use the same key Nothing proves however that this security is not for cipher and decipher messages. The key must be preserved compromised in a near future because there is an accelerated secret by the parties of a communication. So in a network of evolution of the software and the specific hardware. So, many n people wanting to communicate in a confidential way with cryptographic schemes in use today would be broken with a cryptosystems of symmetric encryption, it is necessary that either unanticipated advances in hardware and algorithm or the keys are distinct. Precisely, it is necessary to create and the advent of quantum computers. distribute n( n − 1) 2 keys which are distinct and secret. As Another solution to the delicate problem of distribution of we can remark, the cryptosystems of symmetric encryption keys met in cryptography consists at using the laws of the suffers from the problem of creation and distribution the quantum physics. It is precisely to place at the disposal of keys. This problem is mainly solved by the installation of the security of computing systems a Quantum Cryptography cryptosystems of asymmetric encryption (A. J. Menezes, protocols in order to carry out a task of exchanged keys with 1996). a great security. Quantum Cryptography has been proven mmm secure even against the most general attack allowed by the This work is partially supported by the Academy Hassan II of Sciences and laws of physics and is a promising technology for adoption in Technology (Morocco). realistic cryptographic applications. Quantum Cryptography Copyright © 2010 HyperSciences_Publisher. All rights reserved 59 www.hypersciences.org International Journal of Universal Computer Sciences (Vol.1-2010/Iss.2) Elboukhari et al. / Quantum Key Distribution Protocols: A Survey / pp. 59-67 allows two parties to expand on a secret key that they have the system security by applying specific methods for key previously shared. Various quantum cryptographic protocols distribution under various attacks. have been proposed in order to achieve unconditional security. The first one who examined the security of quantum cryptosystems was Lutkenhaus (N. Lutkenhaus, 1996). In (E. In this article, we give in details the descriptions of the Biham and T. Mor, 1997a, b) Biham and Mor presented a famous Quantum Cryptography protocols: BB84, B92 and method of resolving collective attack. Mayers and Salvail (D. E91. Also, we provide a short presentation of some others Mayers and L. Salvail, 1994), Yao (A.C.-C. Yao, 1995) and recent protocols. Mayers (D. Mayers, 1996) based their research on BB84 Protocol (C.H. Bennett and G. Brassard, 1984), believing that The organization of the remainder of our paper is as follows. this method could provide unconditional security and resist In section II, we introduce the state-of-the-art of Quantum various attacks. In the article (C.H. Bennett, 1996) Bennett et Cryptography. The description of the protocols BB84, B92, al. examined the security of even–odd bits of Quantum E91 and others protocols is given in section III. Finally, we Cryptography. conclude the paper in section IV. Despite the development of Quantum Key Distribution 2. STATE OF THE ART OF QUANTUM protocols (QKDP), after 20 years, a group of scholars CRYPTOGRAPHY asserted that although quantum cryptosystem based on the QKDP can achieve unconditional security, its key generation Mathematicians have searched for ages, for a system that is not efficient in practice because the qubits transmitted in would allow two people to exchange messages in perfect the quantum channel cannot be completely employed. For privacy. Quantum Cryptography was born in the early example, out of 10 qubits, only 5 qubits are used for key seventies when Stephen Wiesner wrote the article "Conjugate generation. Also, its key distribution applies one-time pad Coding"(S. Wiesner, 1983), was rejected by IEEE method, and the length of the key must be the same as that of Information Theory but was eventually published in 1983 in the plaintext, so the number of qubits required far exceeds the SIGACT News (15:1 pp. 78-88, 1983). Stephen Wiesner length of plaintext. So, the cost of frequent transmission of showed in his paper how to store or transmit two messages bulk messages is much too high. Consequently, the new idea by encoding them in two “conjugate observables”, such as of Quantum Secure Direct Communication (QSDC) is linear and circular polarization of light, so that either, but not proposed. A QSDC protocol transforms plaintext to qubits to both, of which may be received and decoded. His idea is replace the key, and transmits the messages via the quantum illustrated with a design of unforgeable bank notes. channel. This reduces the number of qubits used, thus enables automatic detection of eavesdroppers. The ongoing development of quantum cryptosystems thereafter was primarily the result of the efforts of Charles Beige et al. (A. Beige, 1999) was initialized the elaboration Bennett and Gilles Brassard. Most quantum cryptographic of QSDC Protocol. In their scheme, the secure message key distribution protocols developed during that time were comprises a single photon with two qubit states; it becomes based on Heisenberg’s Uncertainty Principle and Bell’s read-only after a transmission of an extra classical message Inequality. Others employed the quantum non-localization, via a public channel for each qubit. Later Boström and such as the cryptosystem developed by Biham et al. (E. Felbingeer developed a Ping-Pong QSDC Protocol (K. Biham, 1996). Users store a particle in the quantum memory Bostro, 2002) that adopts the Einstein–Podolsky–Rosen of the sending center, such that the users of the same center (EPR) pairs (A. Einstein, 1935) as the quantum information are assured secure communication. Phoenix et al.( S.J.D. carriers. In this protocol, the secure messages are decoded Phoenix, 1995) introduced a method of developing a during transmission, and no additional information needs to quantum cryptographic network rather than adopting be transmitted. A QSDC scheme using batches of single quantum non-localization. Huttner and Peres employed non- photons that acts as a one-time pad (F.-G. Deng and G.L. coupled photons to exchange keys (B. Hutter and A. Peres, Long, 2004) is proposed by Deng et al. in 2004 and in 2005 1994), and Huttner et al. also applied a weak correlation to Lucamarini and Mancini presented a protocol (M. reduce significantly the level of tapped information (B. Lucamarini and S. Mancini, 2005) for deterministic Hutter, 1995). Wiesner used bright light to construct a communication without applying entanglement. Wang et al. quantum cryptosystem (S. Wiesner, 1993). proposed a QSDC approach that uses single photons, of which the concepts were resulted from the order The early quantum cryptosystems developed in the 1980s and rearrangement and the block transmission of the photons (J. 1990s however lacked complete facilities of research on the Wang, 2006). security of key distribution protocols. An eavesdropper in these systems was assumed to be able to adopt only simple 3. PROTOCOLS OF QUANTUM CRYPTOGRAPHY wiretap methods but quantum mechanics can in practice support more complex methods. Applying a separate method 3.1 BB84 Protocol to manage each possible attack is quite difficult and numerous research scholars devote themselves in enhancing This protocol (C.H. Bennett and G. Brassard, 1984) was elaborated by Charles Bennett and Gilles Brassard in 1984. It 60 International Journal of Universal Computer Sciences (Vol.1-2010/Iss.2) Elboukhari et al.